From: Trond Myklebust <trond.myklebust@fys.uio.no>
Subject: Re: flock and lockf over NFS and the 'pid' in lockd requests.
Date: Sun, 29 Apr 2007 22:13:53 -0400
Message-ID: <1177899233.6400.58.camel@heimdal.trondhjem.org>
References: <17973.19011.690165.95878@notabene.brown>
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Cc: nfs@lists.sourceforge.net
To: Neil Brown <neilb@suse.de>
In-Reply-To: <17973.19011.690165.95878@notabene.brown>
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On Mon, 2007-04-30 at 11:45 +1000, Neil Brown wrote:
>  Currently an flock and an fcntl lock on the one file will both be sent
>  to the lockd server and it will appear to be a conflict.  We can tell
>  lockd that it isn't a conflict by setting the 'pid' field in the lock
>  requests to some constant (e.g. 0, or 42 or whatever).
>  As no genuine conflicts are ever sent to a server, it is always safe
>  to just send a constant pid.  The pid is only used for lockd to
>  mediate locking requests between processes on the same client.  Now
>  that the lockd client never depends on the server for that mediation,
>  there is no need to send the pid.

??? On the contrary. Genuine conflicts are currently resolved by the
server and the server alone. We do admittedly call do_vfs_lock() with
the ACCESS flag set, but that doesn't set a lock. It is quite possible
for 2 processes to pass the do_vfs_lock() call, but then conflict on
actually setting the lock.

IOW: afaics your patch will fundamentally break posix/fcntl() locks.

Worse, it means that unlocking the flock() may result in an automatic
clearing of all posix/fcntl() locks...

Cheers
  Trond


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